My minivan's engine seems to misfire irregularly but more often when it is hot. I had a mechanic checked and he said it was NOT misfiring (checked ignition wires/cylinders) but it was the ac expansion valve in the front. It appears to be closing/sticking and the pressure was too high. He evacuated and filled to the right amount of 134. Symptoms got better, but it still happens, especially when it is hot outside.

He said it would be about $120 labor + $30 parts to evacuate, replace expansion valve, and refill.

Question: Does a sticking ac expansion valve in the front cause this behavior/symptom?

Not very sure but should be able to simply run front only and tell if there is a failure of front only or not. Feel lines for temps or use an IR thermometer,

T

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Hey - if this vehicle isn't running properly as described "misfiring" why is A/C involved? Get code readings which should be able to put out a code # indicating which cylinder or multiple misfires. Do keep in mind codes tell you the circuit with a problem not what the problem is or a part to replace.......

Easy to test. Next time it happens, turn off the AC or unplug the compressor clutch, if the problem goes away than there is something happening when the AC is on. Could be as simple as too slow an idle for the compressor load, For the Tx valve to cause a problem, the only thing I can see is either stuck closed and the high side is too high (I which case you would be looking for safety valve or blow off opening) or over charged and stuck open, where you could have liquid refrigerant "slogging" the compressor. Both are unlikely. Far more likely is you are feeling viberation and thinking it is a "miss".